The invention relates generally to cutting apparatus and in particular to an improved tooth geometry in a welded edge band saw blade.
The terms used to describe the geometry of a saw blade tooth, for example the rake angle, the wedge angle, the relief angle, etc., are defined in International Standard ISO 4875/1-1978. The terms used herein to define tooth geometry are in accordance with the definitions in ISO 4875/1-1978.
For most of the past fifty years, the geometry of a band saw blade tooth has remained substantially unchanged. And during the past fifty years it has become well known that a good tooth geometry requires a tradeoff between many conflicting parameters. In particular, a tooth should have a large mass for strength and to conduct heat away from the cutting edge or tooth tip. This corresponds to a large wedge angle and a small relief angle. A large wedge angle and small relief angle also give the tooth greater resistance to shock and vibration, and in the case of a welded edge band saw blade, a greater resistance to stripping or shearing.
Yet at the same time, the relief angle should be maintained as large as possible so that the wear properties of the tooth are not substantially diminished. Wear in connection with a blade tooth is denoted by a flat which replaces the originally sharp tooth tip as the blade is used. As the flat increases in area, the force applied to the blade to maintain the same pressure on the workpiece must be correspondingly increased.
In the welded edge band saw blade wherein a tooth tip portion of a high hardness, high strength material is welded to a band base of a strong, flexible material, there is, in addition, the requirement that the welds between the tips and the rest of the blade be strong and hence have a significant linear length. This is particularly important because these band saw blades operate at high cutting speeds utilized in today's high speed, heavy duty, band saw cutting equipment. The desired result in this context is a welded edge band saw blade in which the area of the weld for each tooth is as great as possible. And this requirement is generally satisfied by a tooth geometry having a large mass which, as noted above, also e.g., removes substantial heat from the cutting surface.
The rake angle of the earlier saw blades including band saw blades was generally zero degrees. This is typically called a regular or standard tooth geometry, i.e. a tooth which has a rake angle of zero degrees and a full rounded gullet. It has also become well known that a second configuration of tooth geometry, having a positive rake angle, reduces the cutting stress and generally provides an increased cutting rate. This is the hook tooth form. However the reduction in cutting stress was heretofore available only at the expense of tooth mass. Thus, in the regular tooth, the wedge angle was typically about 54.degree. or 55.degree. and the relief angle was typically 35.degree. or 36.degree.. When a positive rake angle was introduced, it was primarily at the expense of the wedge angle, it also being well known that the minimum acceptable relief angle was substantially 30.degree.. Thus, in a well designed hook tooth, the positive rake angle was typically 5.degree.-10.degree., the wedge angle was 50.degree.-51.degree., and the relief angle was greater than or equal to 30.degree.. As a result, in a hook tooth the mass of the cutting tooth was reduced and hence the heat conduction and strength properties of the tooth were also reduced. Nevertheless, however, the hook tooth design is advantageous, particularly in work hardening metals, and has been successfully used by many manufacturers.
The requirement of an at least minimum relief angle of 30.degree. alluded to above in the hook tooth geometry, meets the minimum requirement for gullet area to remove the chips as they are being formed in a cutting operation. If the gullet area were too small, the tooth, as it cuts through a workpiece, could pack the gullet area with chips; and if the gullet area became packed prior to exiting the workpiece, the chip material within the gullet either would force the blade away from the workpiece or would require additional force to maintain the blade in contact with the workpiece. In addition, depending upon the chip configuration, increased loading, and even binding, of the blade can occur. Therefore in high speed, heavy duty band sawing, an adequate gullet area is a necessary requirement.
The geometry of prior saw teeth further makes it clear that the gullet space, for high speed cutting applications, not only must be large in order to accommodate a generous filling of chip material but should also be configured to allow that chip material to be easily removed from the gullet as the tooth exits from the workpiece. For this reason, the gullet bottom of a standard tooth has a generally well rounded, relatively large space so that the chip materials contained therein will fall away with relative ease. Even so, however, in those instances wherein the chip material either breaks or forms a tightly wound spiral configuration while being removed from the workpiece, the chip material may form a cylinder of sufficient diameter to engage the entire circular bottom of the gullet space. Thus, designers have provided not only large gullet spaces but a gullet space having a large radius bottom shape. The large area gullet tends to dictate, in prior tooth geometries, the relatively large relief angle and where a positive rake angle is employed, a concomitant smaller wedge angle.
Despite the availability of known and useful, commercially accepted standard tooth geometries, various applications require special blade tooth geometries in order to meet their operating specifications. Thus, in the early 1940's, it was suggested that the regular tooth geometry be modified after hardening by grinding the tooth tip at a primary relief angle of 15.degree.-20.degree.. (See for example Stevens U.S. Pat. No. 2,431,517). In Stevens, a "regular tooth" is purposely cut back at its tip so that the primary relief angle, that is, the relief angle at the tip of the tooth, is between about 15.degree. and 20.degree. and a secondary relief angle, that is, the original relief angle of the tooth before being cut back, is about 36.degree.. Stevens claims in U.S. Pat. No. 2,431,517 that the reduced primary relief angle provides outstandingly improved qualities both from the standpoint of useful life and cutting speed. The Stevens blade however, because the relief angle is between 15.degree. and 20.degree., would result in significantly shortened life for a band saw blade.
Another application employing a shallow first relief angle is disclosed in Cowley, U.S. Pat. No. 3,416,579, in which the initial starting teeth of a hack saw blade each have a small first relief angle of between 7.degree. and 18.degree.. This small relief angle provides easy starting on thin materials but is not adapted to provide the advantages of the present invention. The Cowley teeth are otherwise "regular teeth" insofar as they have a zero degree rake angle.
It is therefore an object of the invention to provide an improved tooth geometry for a welded edge band saw blade which has a positive rake angle and increased tooth mass, while maintaining a large, gullet space. Other objects of the invention are a strong tooth tip configuration and a large heat transfer tooth mass, which lead to a high cutting rate and long life. Yet a further object of the invention is a gullet space configuration which provides good chip removal. Further objects of the invention are a tooth geometry which can be easily manufactured, which maintains a high cutting rate and a low cutting stress associated with positive rake angle tooth geometries, which maintains concurrently a large gullet area for heavy duty applications, and which provides a long weld line for high shearing strength and reliability.